The invention relates generally to semiconductor fabrication and, more specifically, to a method and system for performing radius of curvature measurements on a two-dimensional curved feature to accurately determine the feature""s diameter and circularity. Critical dimension scanning electron microscopes xe2x80x9cCD-SEMxe2x80x9d are often used to perform measurements on semiconductor features during fabrication (e.g. contact hole diameter, line widths, etc.). Numerous scans, typically 32 scans or 64 scans, of the feature are performed in the x direction and/or in the y direction. For contact holes, the largest x measurement and the largest y measurement are recorded as the assumed diameter. Comparison of these two assumed diameter measurements gives a limited indication of circularity.
For example, some CD-SEMs can measure the diameter of contact holes in both the y and x directions. The measurements represent the maximum space length of the series of scans that are rastored over the contact hole. This technique is suitable for contact holes that are highly circular and exhibit little edge roughness. A more accurate measurement is obtained by performing scans in the vertical and horizontal directions and averaging the diameters. The ratio of the two numbers can also give information about the circularity of the feature. However, the results are often inaccurate given a feature that is highly non-circular.
Due to typical irregularities on the edge of a feature such as a contact hole in a semiconductor device, this numerous scan approach often results in erroneous measurements. Further, numerous scans cause charging and/or contamination buildup on a feature""s edge. This may cause the apparent feature size to change. Also, the practice of using the largest measurement as the assumed diameter will give an erroneous result if a feature is a non-circular contact hole. A more accurate method is desired.
An exemplary embodiment of the invention is a method and system for determining a radius of curvature of a two-dimensional curved feature. The system includes an image/scan acquisition device for obtaining images/scans of said curved feature. A processor is coupled to the image/scan acquisition device for receiving the images and converting the images to n sets of coordinates corresponding to points on the perimeter of the curved feature. The processor chooses at least three sets of said coordinates to define at least one group and fits each set of said coordinates from each group to an equation for a circle and determines a radius of curvature by solving each equation simultaneously. A storage device is coupled to the processor for storing processor data. An output device is coupled to the processor for outputting processor data.